Some further research, and I have even found some open-ended Toyota 12x1.5 shank style lugs, http://www.ezaccessory.com/Toyota_Lexus_OEM_Mag_Lug_Nuts_Open_End_p/98-0003oe.htm, $2 a piece.
Has anyone ever found a Z-style shanked lugnut in a different thread, specifically 12x1.5 instead of the stock 1.25? My 510 racecar has long, hardened wheels studs in 12x1.5, but I have a set of 280zx wheels I'd like to use, and can't find any lugnuts that fit the stepped/shouldered lugnut hole other than the OE ones. I'm prepared to cut off the end of a closed nut if neccesary. Thanks, Troy